Does Ubuntu Desktop 32 Bit support more than 4GB memory WITHOUT changing anything (Without having to activate PAE via compiling kernel or anything similar). Will installing the 32 Bit Ubuntu on the machine be enough to detect the additional memory automatically. If yes, will this work if I add more than 4GB with a 32Bit Ubuntu already with 4GB Ram.
One example would be to have 8GB Ram with Ubuntu 32 Desktop.

My Motherboard supports up to 8GB RAM and it has 32 Bit and 64 Bit support (It is the intel DP35DP)

There was the issue which I posted in launchpad about the LiveCD/LiveUSB that when installing from them you would get a black screen if you had a integrated video card and an Nvidia card. The solution was to disconnect/connect the VGA or HDMI cable from the Nvidia card. At least until a solution appeared. The other one was at least 4 system freeze appeared to me on the 64bit one. I know this would be solved in a couple of weeks but for the time I would use the 32bit until I test again when 12.04.1 comes out.
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Luis Alvarado♦Apr 30 '12 at 1:43

7 Answers
7

Ubuntu 10.04 and newer should support PAE out of the box, and most processors produced in the last twelve years do too, so in theory it should work fine.
If you're trying to install Karmic or older, you may need to enable PAE yourself, as per this wiki article.

It may also be necessary to switch certain options in your BIOS, such as "Software Memory Hole".

A 32-bit computer has a word size of
32 bits, this limits the memory
theoretically to 4GB. This barrier has
been extended through the use of
'Physical Address Extension' (or PAE)
which increases the limit to 64GB
although the memory access above 4GB
will be slightly slower.

So if i install Ubuntu 32bit on my 4GB computer. Then put in another 4GB for a 8GB total. It will read it without chaging ANYTHING at all.
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Luis Alvarado♦Jan 4 '11 at 19:01

You should at least check which kernel you're running first, by issuing the command uname -a. I'm pretty sure PAE would be needed to use the whole 4 GB in the first place. @CYREX
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oKtosiTeJan 4 '11 at 19:14

I have 4GB right now and i just installed the ubuntu desktop 32bit normal one found on the website. When i cat proc/meminfo i get the total like this MemTotal: 4054012 kB The cpu shows pae when i do this: cat /proc/cpuinfo | grep pae
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Luis Alvarado♦Jan 4 '11 at 21:46

Your kernel needs to support it too. Does the name of the kernel as shown in uname -a include anything like PAE or bigmem? @CYREX
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oKtosiTeJan 4 '11 at 23:11

As Scaine commented on one of the other answers, you could check with System > Administration > System Monitor. Even if it's not in the kernel's name, it may still be supported. @CYREX
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oKtosiTeJan 5 '11 at 20:41

Ubuntu 10.04 LTS (Lucid Lynx) to Ubuntu 12.04 LTS (Precise):
Both the CD and DVD installer of Ubuntu automatically installs the PAE enabled kernel if it detects more than 3 Gb of available memory. In the case of the liveCD, a working network connection is required, since the PAE enabled kernel packages are not present on the CD.

PAE above is the best route.
For your information, This week I took advantage of cheaper UK 8Gb RAM (£20.00!) modules for my current AMD X2 Dual core with 4Gb DDR3 (1333) memory, replacing the 2 modules with one single 8Gb, but found then I only had some 3.7Gb in memory using (the System Tool). A quick read here on askubuntu and the said above article https://help.ubuntu.com/community/EnablingPAE using PAE, a quick install via Terminal, and a reboot, then gave me 8Gb.

For the present, I'm only running 11.04 on 1 of 3 comps (others run 12.04), but will upgrade to the latest when time prevails. I merely wanted the memory to work now and PAE was not installed on my 11.04. It took me as long as it takes to download via Terminal as in the above help "Enabling PAE manually" section of the article. If PAE supports upto 64Gb as it says, then I'll take the 16Gb RAM route.

I suggest anyone looking to upgrade similar at 11.04 stage, follow the above.

Both the CD and DVD installer of Ubuntu 10.04 automatically installs the PAE enabled kernel if it detects more than 3 Gb of available memory. In the case of the liveCD, a working network connection is required, since the PAE enabled kernel packages are not present on the CD.

And I installed 32-bit 10.10 on a server with 4Gb of RAM two days ago. Didn't have to do anything - it just worked. If you run system/administration/system monitor after your install, you can check the "system" tab to confirm that the pae kernel auto-installed.
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ScaineJan 5 '11 at 0:20